Interleukin-1.

Interleukin-1 (IL-1) is a polypeptide that is produced following infection, injury, or antigenic challenge. Although the macrophage is a primary source of IL-1, epidermal, epithelial, lymphoid, and vascular tissues synthesize IL-1. When IL-1 gains access to the circulation, it induces a broad spectrum of systemic changes in neurologic, metabolic, hematologic, and endocrinologic systems. However, because IL-1 lacks a signal peptide, a considerable amount of the IL-1 that is synthesized may remain associated with the cell, particularly as part of the plasma membrane; moreover, membrane-associated IL-1 is biologically active, especially in its ability to participate in lymphocyte activation and mesenchymal tissue remodeling. There are two gene products coding for IL-1:IL-1-beta and IL-1-alpha. The spectrum of biologic activities of IL-1 are induced by both forms. IL-1 activates lymphocytes and plays an important role in the initiation of the immune response. Receptors for IL-1 recognize both forms, but receptors are scare and their affinities often do not match the potency of the biologic response. The most consistent property of IL-1 is up-regulation of cellular metabolism and increased expression of several genes coding for biologically active molecules. IL-1 is a highly inflammatory molecule and stimulates the production of arachidonic acid metabolites. IL-1 also acts synergistically with other cytokines, particularly tumor necrosis factor. The multitude of biologic responses to IL-1 is an example of the rapid adaptive changes that take place to increase the host's defensive mechanisms.